Electrical actuators are used in automation technology for control of machine, or apparatus, parts serving for handling or monitoring. A preferred example of such a part is a control element, such as a valve, a gate, a throttle or a baffle. Depending on the control element, the actuation, respectively displacement, is a rotary, translational or a combined rotary, translational movement.
Electrical actuators for these machine, or apparatus, parts must be designed such that they can transmit high torques (30-500,000 Nm) at low RPM (4-180 RPM), wherein the transmitted torque must be highly constant during small angles of rotation. In the case of known actuators, the torque transmission between electric motor and the machine, or apparatus, part occurs via a speed reduction transmission, which, depending on application, can be very differently embodied. The speed reduction transmission is necessary, among other things, in order to convert the high RPM of the electric motor into the desired highly constant output RPM for actuating the machine, or apparatus, part. Applied as speed reduction transmission can be any suitable type of transmission. Examples include bevel or spur gear transmissions, worm gear transmissions, superimposed transmissions or lever transmissions. Auma Riester GmbH+Co. KG manufactures and sells actuators suitable for the most varied of applications. Thus, torque can amount up to 32,000 Nm in the case of completely revolving, rotary drives, while, in the case of rotary drives with less than 360 degree range, torques up to 500,000 Nm can be implemented.
By way of example, the principle of construction of a known actuator will now be described: For reducing the RPM of the electric motor to the output RPM, with which the machine, or apparatus, part is actuated, there is combined with a planetary gear transmission a worm gear transmission having a worm shaft, a worm and a worm gear, or wheel. In order to assure that the worm gear transmission remains in the desired rest position in the case of shutdown of the electric motor, the worm gear transmission is self-locking. Worm shaft and hollow output shaft with worm gear, or wheel, turn usually in ball bearings, respectively dry sliding bearings.
The worm is arranged shiftably on the worm shaft between two measuring spring packages, so that the worm experiences a translational movement relative to the worm shaft in the case of a torque to be transmitted. This shifting, which is a measure for torque to be transmitted, is forwarded to a control unit. The transmission interior is filled with lubricant, so that maintenance free operation is assured over an extended period of time.
Depending on the type of construction of the machine, or apparatus, part, the rotary drive must be turned off in the end positions path dependently, or torque dependently. For this, usually two independent measuring systems are provided in the control unit, namely a path circuit and a torque circuit, which measure the traveled actuation path, respectively the torque applied on the output shaft. The reaching of a desired end position is signaled to the control unit via a switch, and the control unit then turns the electric motor off.
In order to fulfill a safety standard specified in automation technology, the actuator must be able to be operated in an emergency via a separately actuatable, adjusting wheel. This adjusting wheel is used, moreover, also, for example, in the case of start-up of the actuator. The adjusting wheel is usually a handwheel, which is manually actuated by operating personnel, so that the machine, or apparatus, part is brought into a desired position. The adjusting wheel can, furthermore, be a crank or some other lever mechanism, e.g. a detent mechanism.
For the purpose of isolating hand operation and motor operation, a coupling mechanism is provided. The coupling mechanism is usually so embodied and/or arranged that, in motor operation, the rotor is directly coupled with the output shaft and the adjusting wheel is uncoupled, while in hand operation, respectively manual actuation, the output shaft is coupled with the adjusting wheel and the rotor is uncoupled. In this way, isolation of motor operation from hand operation is achieved. The coupling mechanism is preferably embodied in such a manner that the adjusting wheel is automatically uncoupled from the rotor shaft, as soon as the actuator works in motor operation—motor operation thus has precedence over hand operation.
Disadvantageous in the case of known actuators with a manually actuatable adjusting wheel is that a spatial isolating of adjusting wheel and actuator is only possible via relatively complex, supplemental constructions. These supplemental constructions mean increased manufacturing costs and supplemental space requirement.